Glasses prepared following a sol-gel route must be thermally treated to evacuate solvent and organic radicals. They often undergo phase transitions in the same temperature range where the weight tosses occur. When applied to these systems, conventional differential scanning calorimetry (DSC) may lead to deceiving interpretations. In this paper the transformations of a sol-gel lithium triborate glass, annealed up to 500 degrees C, have been investigated by Modulated DSC (MDSC). We show how the reversing heat flow signal obtained by temperature modulation may give valuable information. Upon annealing, the system undergoes phase separation and partial devitrification to give crystalline lithium diborate. A careful comparison with the misleading conclusions offered by conventional DSC is performed.